NASA’s Hubble Takes Census of Early Galaxies
Using the Hubble Space Telescope, astronomers have discovered seven previously unseen galaxies that formed over 13 billion years ago – a time when galaxies were just beginning to form. The new discovery has provided researchers with a “statistically robust” sample of early galaxies, revealing how abundant such galaxies were at the beginning of the universe.
The images come from a Hubble survey of the Ultra Deep Field (UDF), a patch of sky that has been studied intensely. Astronomers used Hubble’s Wide Field Camera 3 (WFC 3) instrument to obtain the “deepest” near-infrared images of any Hubble observation.
The findings, which are collected in a paper that has been accepted for publication in The Astrophysical Journal Letters, show a smooth decline in the number of galaxies when looking back to only 450 million years after the big bang. The observations support the hypothesis that galaxies formed continuously over time and could have provided enough radiation to re-ionize the universe.
“Our study has taken the subject forward in two ways,” said Richard Ellis, the team leader of the research and an astronomer at the California Institute of Technology. “First, we have used Hubble to make longer exposures. The added depth is essential to reliably probe the early period of cosmic history. Second, we have used Hubble’s available color filters very effectively to more precisely measure galaxy distances.”
One of the galaxies spotted by the new Hubble survey could even be the furthest galaxy yet discovered. It’s redshift indicates its light has just reached Earth from only 380 million years after the big bang. The previous record holder, seen just 420 million years after the big bang, was announced just one month ago.
The new survey also shines light on the debate over whether early galaxies could have provided enough radiation to re-ionize the universe by warming the cold hydrogen that formed after the big bang. Astronomers believe that e-ionization made the universe transparent to light.
“Our data confirm re-ionization was a gradual process, occurring over several hundred million years, with galaxies slowly building up their stars and chemical elements,” said Brant Robertson, an astronomer at the University of Arizona. “There wasn’t a single dramatic moment when galaxies formed. It was a gradual process.”
(Image courtesy NASA, ESA, R. Ellis (Caltech), and the UDF 2012 Team)